Tuesday, June 30, 2020

A broad-leaved forest grass that flowers twice

Dichanthelium latifolium

Nowadays, when I hike among the shaded tree-lined paths of some park in New Jersey, i invariably encounter Microstegium vimineum as it grows in luxuriant carpets along the sides of the trail and into the deeper canopy.

This was at first the case last Thursday, when we went exploring in the Watchung Reservation, and I resigned myself to photographing more of the invasive grass.

Dichanthelium latifolium

Thus it was a pleasant surprise when I spotted an interesting grass nestled in the shady base of one of the trees. It had much larger leaves than stiltgrass, and it also had airy panicles that ended in tiny spikelets. The blades also had distinctive cordate bases, and were quite wide.

I managed to identify the species as  Dichanthelium clandestinum, one of the rosette panic grasses.

Dichanthelium latifolium

This species lives in forests, and has an unusual flowering behavior.

Near the beginning of the season, it produces "normal" flowers which are pollinated when open ("chasmogamous"). Then later in the season, the same individual has closed flowers hidden in the sheaths that will be self-pollinated ("cleistogamous").

Dichanthelium latifolium

The evolutionary advantage of cleistogamy is that the grass does not need to expend a lot of energy into the production of flower accessory structures, and this mode of flowering seems to prevalent in some plants when they are stressed. However, its disadvantage is that it dampens genetic diversity in the population due to self-fertilization.

Dichanthelium latifolium

It was quite nice to find such a new species, and I'll be sure to keep my eyes open for more grasses from the genus  Dichanthelium is future hikes.

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